I would get them out of the petri dish to start. That is way, way too many worms to have in a petri dish. I hatch out about a thousand at a time, but have never hatched as many as you have going. For a thousand, I use an 18" by 18" tray and feed chow in long thin strips. Personally, I would seperate them out into 4 or 5 trays with that many. For a thousand, I run thin strips of chow from one end of the tray to the other, leaving about 2 inches between the strips. When the food is eaten or dries up, I place another strip next to the one that they are on, and they generally migrate over to the new strip.
If you use a soft paintbrush, you should be able to carefully remove worms over to a new container without crushing them. It will take some careful work...
What a pain in the butt for you!
Heika